view tests/test-histedit-no-change.t @ 33207:895ecec31c70

revlog: add an experimental option to mitigated delta issues (issue5480)

The general delta heuristic to select a delta do not scale with the number of
branch. The delta base is frequently too far away to be able to reuse a chain
according to the "distance" criteria. This leads to insertion of larger delta (or
even full text) that themselves push the bases for the next delta further away
leading to more large deltas and full texts. This full text and frequent
recomputation throw Mercurial performance in disarray.

For example of a slightly large repository

  280 000 files (2 150 000 versions)
  430 000 changesets (10 000 topological heads)

Number below compares repository with and without the distance criteria:

manifest size:
    with:    21.4 GB
    without:  0.3 GB

store size:
    with:    28.7 GB
    without   7.4 GB

bundle last 15 00 revisions:
    with:    800 seconds
             971 MB
    without:  50 seconds
              73 MB

unbundle time (of the last 15K revisions):
    with:    1150 seconds (~19 minutes)
    without:   35 seconds

Similar issues has been observed in other repositories.


Adding a new option or "feature" on stable is uncommon. However, given that this
issues is making Mercurial practically unusable, I'm exceptionally targeting
this patch for stable.

What is actually needed is a full rework of the delta building and reading
logic. However, that will be a longer process and churn not suitable for stable.

In the meantime, we introduces a quick and dirty mitigation of this in the
'experimental' config space. The new option introduces a way to set the maximum
amount of memory usable to store a diff in memory. This extend the ability for
Mercurial to create chains without removing all safe guard regarding memory
access. The option should be phased out when core has a more proper solution
available.

Setting the limit to '0' remove all limits, setting it to '-1' use the default
limit (textsize x 4).

test for old histedit issue #6:
editing a changeset without any actual change would corrupt the repository

  $ . "$TESTDIR/histedit-helpers.sh"

  $ cat >> $HGRCPATH <<EOF
  > [extensions]
  > histedit=
  > EOF

  $ initrepo ()
  > {
  >     dir="$1"
  >     comment="$2"
  >     if [ -n "${comment}" ]; then
  >         echo % ${comment}
  >         echo % ${comment} | sed 's:.:-:g'
  >     fi
  >     hg init ${dir}
  >     cd ${dir}
  >     for x in a b c d e f ; do
  >         echo $x > $x
  >         hg add $x
  >         hg ci -m $x
  >     done
  >     cd ..
  > }

  $ geneditor ()
  > {
  >     # generate an editor script for selecting changesets to be edited
  >     choice=$1  # changesets that should be edited (using sed line ranges)
  >     cat <<EOF | sed 's:^....::'
  >     # editing the rules, replacing 'pick' with 'edit' for the chosen lines
  >     sed '${choice}s:^pick:edit:' "\$1" > "\${1}.tmp"
  >     mv "\${1}.tmp" "\$1"
  >     # displaying the resulting rules, minus comments and empty lines
  >     sed '/^#/d;/^$/d;s:^:| :' "\$1" >&2
  > EOF
  > }

  $ startediting ()
  > {
  >     # begin an editing session
  >     choice="$1"  # changesets that should be edited
  >     number="$2"  # number of changesets considered (from tip)
  >     comment="$3"
  >     geneditor "${choice}" > edit.sh
  >     echo % start editing the history ${comment}
  >     HGEDITOR="sh ./edit.sh" hg histedit -- -${number} 2>&1 | fixbundle
  > }

  $ continueediting ()
  > {
  >     # continue an edit already in progress
  >     editor="$1"  # message editor when finalizing editing
  >     comment="$2"
  >     echo % finalize changeset editing ${comment}
  >     HGEDITOR=${editor} hg histedit --continue 2>&1 | fixbundle
  > }

  $ graphlog ()
  > {
  >     comment="${1:-log}"
  >     echo % "${comment}"
  >     hg log -G --template '{rev} {node} \"{desc|firstline}\"\n'
  > }


  $ initrepo r1 "test editing with no change"
  % test editing with no change
  -----------------------------
  $ cd r1
  $ graphlog "log before editing"
  % log before editing
  @  5 652413bf663ef2a641cab26574e46d5f5a64a55a "f"
  |
  o  4 e860deea161a2f77de56603b340ebbb4536308ae "e"
  |
  o  3 055a42cdd88768532f9cf79daa407fc8d138de9b "d"
  |
  o  2 177f92b773850b59254aa5e923436f921b55483b "c"
  |
  o  1 d2ae7f538514cd87c17547b0de4cea71fe1af9fb "b"
  |
  o  0 cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b "a"
  
  $ startediting 2 3 "(not changing anything)" # edit the 2nd of 3 changesets
  % start editing the history (not changing anything)
  | pick 055a42cdd887 3 d
  | edit e860deea161a 4 e
  | pick 652413bf663e 5 f
  0 files updated, 0 files merged, 2 files removed, 0 files unresolved
  Editing (e860deea161a), you may commit or record as needed now.
  (hg histedit --continue to resume)
  $ continueediting true "(leaving commit message unaltered)"
  % finalize changeset editing (leaving commit message unaltered)


check state of working copy
  $ hg id
  794fe033d0a0 tip

  $ graphlog "log after history editing"
  % log after history editing
  @  5 794fe033d0a030f8df77c5de945fca35c9181c30 "f"
  |
  o  4 04d2fab980779f332dec458cc944f28de8b43435 "e"
  |
  o  3 055a42cdd88768532f9cf79daa407fc8d138de9b "d"
  |
  o  2 177f92b773850b59254aa5e923436f921b55483b "c"
  |
  o  1 d2ae7f538514cd87c17547b0de4cea71fe1af9fb "b"
  |
  o  0 cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b "a"
  

  $ cd ..

  $ initrepo r2 "test editing with no change, then abort"
  % test editing with no change, then abort
  -----------------------------------------
  $ cd r2
  $ graphlog "log before editing"
  % log before editing
  @  5 652413bf663ef2a641cab26574e46d5f5a64a55a "f"
  |
  o  4 e860deea161a2f77de56603b340ebbb4536308ae "e"
  |
  o  3 055a42cdd88768532f9cf79daa407fc8d138de9b "d"
  |
  o  2 177f92b773850b59254aa5e923436f921b55483b "c"
  |
  o  1 d2ae7f538514cd87c17547b0de4cea71fe1af9fb "b"
  |
  o  0 cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b "a"
  
  $ startediting 1,2 3 "(not changing anything)" # edit the 1st two of 3 changesets
  % start editing the history (not changing anything)
  | edit 055a42cdd887 3 d
  | edit e860deea161a 4 e
  | pick 652413bf663e 5 f
  0 files updated, 0 files merged, 3 files removed, 0 files unresolved
  Editing (055a42cdd887), you may commit or record as needed now.
  (hg histedit --continue to resume)
  $ continueediting true "(leaving commit message unaltered)"
  % finalize changeset editing (leaving commit message unaltered)
  Editing (e860deea161a), you may commit or record as needed now.
  (hg histedit --continue to resume)
  $ graphlog "log after first edit"
  % log after first edit
  @  6 e5ae3ca2f1ffdbd89ec41ebc273a231f7c3022f2 "d"
  |
  | o  5 652413bf663ef2a641cab26574e46d5f5a64a55a "f"
  | |
  | o  4 e860deea161a2f77de56603b340ebbb4536308ae "e"
  | |
  | o  3 055a42cdd88768532f9cf79daa407fc8d138de9b "d"
  |/
  o  2 177f92b773850b59254aa5e923436f921b55483b "c"
  |
  o  1 d2ae7f538514cd87c17547b0de4cea71fe1af9fb "b"
  |
  o  0 cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b "a"
  

abort editing session, after first forcibly updating away
  $ hg up 0
  abort: histedit in progress
  (use 'hg histedit --continue' or 'hg histedit --abort')
  [255]
  $ mv .hg/histedit-state .hg/histedit-state-ignore
  $ hg up 0
  0 files updated, 0 files merged, 3 files removed, 0 files unresolved
  $ mv .hg/histedit-state-ignore .hg/histedit-state
  $ hg sum
  parent: 0:cb9a9f314b8b 
   a
  branch: default
  commit: 1 added, 1 unknown (new branch head)
  update: 6 new changesets (update)
  phases: 7 draft
  hist:   2 remaining (histedit --continue)

  $ hg histedit --abort 2>&1 | fixbundle

modified files should survive the abort when we've moved away already
  $ hg st
  A e
  ? edit.sh

  $ graphlog "log after abort"
  % log after abort
  o  5 652413bf663ef2a641cab26574e46d5f5a64a55a "f"
  |
  o  4 e860deea161a2f77de56603b340ebbb4536308ae "e"
  |
  o  3 055a42cdd88768532f9cf79daa407fc8d138de9b "d"
  |
  o  2 177f92b773850b59254aa5e923436f921b55483b "c"
  |
  o  1 d2ae7f538514cd87c17547b0de4cea71fe1af9fb "b"
  |
  @  0 cb9a9f314b8b07ba71012fcdbc544b5a4d82ff5b "a"
  
aborting and not changing files can skip mentioning updating (no) files
  $ hg up
  5 files updated, 0 files merged, 0 files removed, 0 files unresolved
  $ hg commit --close-branch -m 'closebranch'
  $ startediting 1 1 "(not changing anything)" # edit the 3rd of 3 changesets
  % start editing the history (not changing anything)
  | edit 292aec348d9e 6 closebranch
  Editing (292aec348d9e), you may commit or record as needed now.
  (hg histedit --continue to resume)
  $ hg histedit --abort

  $ cd ..